It is often useful to sell containers in groups, sometimes called “cluster packs.”
A known way of forming cluster packs is by shrink-wrapping. This method has numerous disadvantages.
From the producer's point of view, shrink-wrapping is an expensive process because it requires considerable energy to heat the shrink-wrap so that it shrinks. Additionally, the shrink-wrap can obscure the labels. The resulting package can be somewhat unattractive.
From the consumer's point of view, shrink-wrap can be difficult to remove. Moreover, it is difficult to remove just one container from the package without undermining the integrity of the containers that remain. As a result, when one pulls a container out of the shrink-wrap, the remaining containers are apt to fall over.
Another alternative is strapping. This avoids the energy expenditure of shrink-wrapping. However, when strapping a rectangular array of bottles, the tension in the strap can sometimes cause a bottle to slip out of its location in the array and become nested at a location that is between the correct locations. This is similar to the manner in which inclusions find their way between lattice points in a crystal lattice.
From the consumer's point of view, strapping is undesirable because once a container is removed, the remaining containers are no longer held in a group. Thus, removal of a container disturbs the integrity of the original container cluster.